This diagram shows the world in profile. With the rim mountains on the top on right and left and the center mountain range at top center. Below the main level of the world is the underworld connected by a huge pillar. The sun rotates about a center that is between the upper and lower worlds.
The plane that the sun rotates in rotates slowly on a north-south axis, completing a revolution in 360 days. Such a revolution is called a year on Mithlond but note that during this year, there are two times when the plane of the sun is parallel to the plane of the world (winter solstice) and twice when is perpendicular to the world plane (summer solstice). Interestingly, the direction of the sun's path around Mithlond is opposite every other solstice. Thus for on summer soltstice the sun rises in the north and sets in the south while for the other it rises in the south and sets in the north. It might help to draw a circle on a sheet of paper with an arrow for the rotation of the sun and rotate the paper around the long axis of the sheet to visualize this. Except for the solstices, the sun travels in a plane angled with respect to the world plane.
Days are essentially 12 hours of night and 12 hours of day but the rim mountains, at 200 miles high, are very tall and do shadow the lands near them. Similarly, the central spine mountains are of similar high and greatly shorten days near them.